Samsung patents optical tool to check if surfaces are perfectly parallel

1. A parallelism measurement optical system module comprising: a polarization beam splitter configured to separate incident light into reference light and measurement light, wherein the polarization beam splitter is configured to be positioned between a first specimen and a second specimen; a mirror positioned on a first surface of the polarization beam splitter and configured to reflect the reference light that has passed through the polarization beam splitter back to the polarization beam splitter; a first quarter wave plate positioned on a second surface of the polarization beam splitter that is perpendicular to the first surface, wherein the first quarter wave plate is arranged to change a polarization state of the measurement light reflected from the polarization beam splitter toward the first specimen, the first quarter wave plate being further arranged to change a polarization state of the measurement light reflected from the first specimen to provide first measurement light; and a second quarter wave plate positioned on a third surface of the polarization beam splitter that is perpendicular to the first surface and parallel to the second surface, wherein the second quarter wave plate is arranged to change a polarization state of the first measurement light that has passed through the first quarter wave plate toward the second specimen, and wherein the second quarter wave plate is arranged to change a polarization state of the first measurement light reflected from the second specimen to provide second measurement light.